Football Club Barcelona have a problem. A big problem. He's 5ft 9in, weighs 11st 8lbs, is 25 years old and comes from Cameroon. He has a big heart, an even bigger gob and an extremely short fuse, and he hates football socks so much that he only wears half of them, stuck on the top of his cotton woollies with Sellotape. His name is Samuel Eto'o and the problem is that his knee is knackered and that without him Barcelona are simply not the same team - as they again proved against Real Madrid last night.

It was the clásico, Spain's twice-yearly Game of the Century, and with Eto'o forced to watch it on French telly, Barcelona fell to a 2-0 defeat at the Santiago Bernabéu that has this morning's Madrid press falling over themselves to print the biggest, most gloatingest headline, from Viking Pride to The Empire Strikes Back and Bath-time for Barça. But whether you chose a longboat, Leia or the loafer - and this column would want the lot - they all meant the same thing: Madrid are back and Barça are in crisis.

Maybe Fabio Capello did mean 50 working days after all. Just a week ago, Madrid turned in a display so wrist-splittingly awful that there were rumours that the Italian with the Franco fixation was going to resign and disappear back to Italy taking his cardigans and funky glasses with him; a display so utterly dire that rather than stopping him, most Madrid fans would have accompanied him to the station, put him on the train and run along the platform as it pulled out, not so much waving their hankies as their index fingers. But, like Superman in a phone box, things change dead quickly round here and eight days later Capello is a hero after goals from Ruud van Nistelrooy and the fast-recovering Raúl condemned Barça to their second defeat in a week.

This was the Madrid Capello really wanted to see - not too much in the way of knocking the ball around but aggressive, quick and tight at the back, with spirit and attitude, dangerous on the break. This was the Madrid that their fans wanted to see, too. With the pace of Robinho, with Iván Helguera back in from the cold, with Fabio Cannavaro finding his feet, and with Sergio Ramos moved to right-back where he's a real asset, Madrid have hope again. Just two points behind Barça, they are starting to look like a side that can compete for the league title. Barcelona, meanwhile, are starting look like a side that will allow them to compete for the league title. They still play the neatest, most fluid football in Spain, they remain top of the table and Leo Messi is truly brilliant but there is something missing. There is, more to the point, someone missing.

Physically, Barça look off the pace with a number of their players complaining about the pre-season tour, while Deco has got steadily worse in recent weeks and Ronaldinho has had a dreadful start to the season, looking slow and unhappy. Captain Caveman Carles Puyol is forever treading a fine line between triumph and disaster, but increasingly falling into the latter, Víctor Valdés makes great saves but does not dominate his penalty area and it is hard to believe that Gianluca Zambrotta was the one everybody really fought over at Juventus's going-down sale. Even Frank Rijkaard has started making strange decisions.

But the single biggest, most decisive difference is Eto'o - the player who, more than any other, is irreplaceable at Barça. Against Madrid last night, Barcelona had the majority of the possession - 65% in the first half, 59% in the second - and their midfield three delivered almost 200 successful passes, compared to fewer than 100 from their opposite numbers in the Madrid team. Likewise, their front three out-passed Madrid's most attacking trio by a third and Messi ran rings round Roberto Carlos and brilliantly nutmegged Cannavaro inside the Madrid penalty area, but all to no avail. It was, as the Spanish put, lots of noise and no nuts. Rather like Jimmy Krankie, in fact.

And there were no nuts because Barcelona missed two wonderful chances, Messi putting one over and Eidur Gudjohnsen hitting the side-netting from the edge of the six-yard box. There were no nuts because after that they seemed to give up, because they were unable to really penetrate Madrid, and because the Icelander simply isn't a replacement for Eto'o; worse, he's not really a replacement for Henrik Larsson. He's scored twice in the league already, both of them vital goals - against Celta and Athletic - but there's none of the pace, the furious hunger, the instinct of Eto'o, none of the mobility, the sharpness in tight spaces or the understanding with his team-mates, none of the desire or ability to chase down defenders or even that insane, pathological will to win.

Barça have now not scored in their last two matches, which may not sound bad - especially coming against Chelsea and Madrid - but it is their worst run in three years. And it is hard to avoid the feeling that had Eto'o been there last night, if he'd been there at Stamford Bridge, things might have been different. He, after all, has scored on each of his last three visits to the Bernabéu and in London last year, he had four in four when he suffered his knee injury and he has scored 50 league goals in two seasons at Barça. Nor does he owe that figure to occasional gluts or pointless goals in dead games. The 68 he has scored in all competitions for Barcelona have been spread over 54 games, scoring the opening goal 34 times. He scored decisive goals in three of Barcelona's four knockout ties in the Champions League last season, including the final, and he scored the goal that clinched the league title in each of the last two seasons. Without him, clinching a third will be much harder.

· Nice to see Graham Poll is not alone. The referee's official report claimed that: "In the 85th minute, the player No23 Beckham, David Robert Joseph, was sent off for a second yellow card." In fact, Becks, who had come on just three minutes earlier, had only been shown one yellow and was still on the pitch.